1. Field of the Invention
The present invention relates to a composition for anti-green algae containing water-soluble free amine chitosan having the anti-algae activity against water-bloom forming algae as an active ingredient and a method for removing green algae using the same.
2. Description of the Related Art
Water-bloom is a result of mass propagation and accumulation of floating algae (phytoplankton) in the water surface of eutrophicated lake or river where water flow is slow, which turns the water color into significant green. The environmental damage caused by such harmful water-bloom observed in between May and October reaches hundreds of billions of Korean Won, which is a significant environmental disaster. Water-bloom is easily developed when the top-water temperature is at least 23° C. for at least 3 consecutive days in the puddles or where the water flows very slowly like in solidified dam, reservoir, lake, golf course water hazard, pond, freshwater fish farm, and fishing spot, etc. Most of green algae found in Korea belong to blue-green algae and the identified algae species are at least 167 species of algae.
Once water-bloom is developed, algae grows in arithmetical progression, so that most of water oxygen is consumed by the algae, resulting in the eutrophication (oxygen deficiency) accompanying bad smell when it becomes worse. Fish in the water are suffering from oxygen deficiency and have difficulty in breathing because of algae attached on gill. Accordingly, the fishes float on the surface of water and cannot be adapted to a rapid change of water temperature, resulting in death. A mass propagation of blue-green algae is frequently observed recently in Nakdong River and Daecheong Reservoir in summer with water color change.
Once water-bloom is developed, the water system is limited in its use as drinking water or in industrial uses. So, it is not only a huge waste of costs but also a significant ecological problem causing other issues in other sectors such as society, economy, and environment as well. The overseas Korean companies are experiencing the direct or indirect damages from water-bloom, and the cases are increasing every year. The case of Azzurri, Argentina, is an example. Precisely, the company was sued for damages by water-bloom in the water treatment plant in Argentina that totaled 550 million dollars (Two of Korean companies which went to the area of Taihu Lake, China, were closed because of water-bloom as of July, 2007).
Another problem caused by the growth of water-bloom forming algae is the toxic cyclic peptide so called microcystin produced by them that might cause a disease in people who swim in the lake or pond where green algae proliferate or who drink water therefrom. The conventional algae control method which aiming at the destruction of algae eventually can rather accelerate the secretion of microcystin where water-bloom is densely developed. Mass secretion of microcystin is not just harmful to the growth of aquatic organisms but also harmful to human.
The water-bloom development is a significant environmental problem not just in freshwater but also in seaside. Water-bloom in the sea is developed by the sedimentation of abnormally proliferated Enteromorpha in shoreline. Water-bloom in the sea is reported from all parts of the world, for example the cases of Chesapeake Bay in USA, Bretagne in France, and Chentao in China are well known. In Japan, see water-bloom has been notified in Tokyo Bay, Seto Inland Sea, and many seaside areas of Kyushu since 1990. Water-bloom in the sea causes the deterioration of seaside landscape, bad smell by the decay of sea algae, and the extinction of fish and shellfish including Manila clam. So, Japanese local governments have been trying to remove and discard green algae with pouring hundreds of thousands of Japanese Yen every year. However, there is no efficient control method yet to remove green algae in the coast which grow every year.
A solution or countermeasure has been sought to minimize the damage by green algae. However, the conventional method or countermeasure established so far might cause problems in the 2nd or 3rd ecosystem and besides it takes a long time to be effective. Followings are the examples of the conventional methods to remove green algae.
First, one of the most conventional methods to remove green algae in freshwater is yellow loess (red clay) dispersal. Yellow loess is a mineral that has a high specific gravity, so that the electrical double-layers of the particle can be significantly condensed and precipitated easily, by which it can coagulate and precipitate green algae down to fresh water or sea water. This method is widely used in Korea to prevent and remove green algae. However, this method can cause secondary environmental pollution, so that it is not widely used in other countries. That is, when yellow loess is sprinkled where water is solidified or where the water flow is slow, micro yellow loess particles are precipitated with destroying other aquatic organisms. In addition, according to the recent report, even the precipitated algae can grow again after the dormant period, which might cause any secondary damage.
Next, a physical green algae control method is to dredge or replace the sedimentary layer to prevent green algae. When all the wastes and pollutants accumulated in the sedimentary layer either on land or fish farm are decomposed, they consumed dissolved oxygen and produce various toxic materials to cause water-bloom. So, as mentioned, this method is to dredge or replace the sedimentary layer. However, this method is not so effective in a big lake or huge dam where green algae are actually observed often.
Another method to control green algae is to build an artificial island or to install a shading net. This method, however, is not so effective in a wide area, either (non-patent reference 1). The deep aeration system that can supply oxygen is usable but only effective in shallow water in about 5 m in depth (non-patent reference 2). Besides, a recently developed device to destroy the membrane of harmful algae by using ultrasonic waves is now on the market (patent reference 1). However, this device also has a disadvantage that is other aquatic organisms might be affected by the strength of ultrasonic eaves. Such physical methods cost a lot to control green algae, suggesting that the usability is very limited.
Considering the above disadvantages of the conventional methods, the present inventors tried the pro-environmental non-toxic, not only to human but also to ecosystem, chitosan on water-bloom forming algae and as a result, the inventors confirmed that the treated chitosan demonstrated anti-algae effect on such water-bloom forming algae but had no toxicity to aquatic organisms, leading to the completion of the invention.